1. Field of the Invention
The present invention relates to a codec system for audio signals, and more particularly, to an audio signal encoding apparatus and a method using the same for optimizing coding parameters through repeated encoding and decoding of audio signals.
2. Description of the Related Art
Real audio signals such as voice signals all have analog characteristics. Analog audio signals should be converted into information of digital signals so that processes such as recording, transmission, and playing may be performed for the audio signals using a computer.
A digital audio encoder-decoder, namely, an audio codec is a device for converting inputted analog audio signals into digital signals. The analog signals are converted into the digital signals by the encoder of the codec. On the contrary, the digital signals are converted into the analog signals by the decoder of the codec so that a user may hear the signals.
Generally, the audio codec receives the analog audio signals, encodes and decodes the received signals, and outputs the same (or very similar) audible signals as the received signals.
At this point, whether to maximize quality of decoded signals or to minimize an amount of information required for encoding the signals should be determined when the analog audio signals are converted into digital audio signals. Further, consideration should be given to balance between the above-described two contradictory goals in designing an audio codec system.
Specifically, quality (substantiality), data rate, complexity, delay time are considered for design requirements of the audio codec system. Design is made by applying different balance between these factors depending on practical application fields and necessities.
Here, the quality (substantiality) is a factor that measures how much an output of the codec is alike an original analog audio signal from an auditive point of view. Quality requirements can be changed depending on application fields. High data rate, high complexity, and long delay time are required to obtain high quality.
The data rate is a factor related to bandwidth capacity and a space for data storage of an entire system. High data rate means that high cost is consumed in storing and transmitting the digital audio signals.
Further, the complexity that performs encoding/decoding processes is a factor related to hardware/software costs of the encoder and the decoder. The complexity of the codec system is determined by complexity requirements depending on application fields.
In a related art, pulse code modulation (PCM) type audio codec has been used for the most simple and general audio codec. The PCM-type encoder performs sampling of analog signals by a predetermined period of time and quantizes sizes of signals to express the signals using predetermined codes.
At this point, loss of information included in original analog signals can be prevented by sufficiently raising a sampling rate during a sampling process but information included in the original signals is essentially lost more or less during the quantization process.
Further, the quantized codes are decoded during a decoding process and signal sequences sampled with respect to discrete time are interpolated so that analog output signals are computed.
That is, whether how much the output signals become similar to the originally received signals is determined depending on how much information is maintained without loss during the quantization process.
Recently, an audio codec system for storing signals in a smaller storage space while obtaining better quality is under development. However, even in that case, the complexity is increased.
General audio encoding applications of a related art assume a real-time or a quasi-real-time audio encoding. Accordingly, the complexity of the encoder is increased and thus the complexity of the decoder is also increased.
As a result, according to the related art, the storage space is increased when the audio signals are stored and transmitted so as to obtain optimized quality and transmission efficiency is lowered in case the storage space is limited.